The present invention relates to flip-chip packages, and more particularly to a universal test coupon for performing pre-qualification tests on organic substrates.
Flip-chip refers to a surface mount chip technology where solder bumps are placed on a chip, and the chip is flipped over and attached to an organic substrate. Depending on the particular application, the substrate may be manufactured with many layers and various structures built both on and between each layer. Examples of the structures include patterns of traces called combs and via chains. There are different vendors of organic substrates, and each vendor may use different materials and technologies to fabricate the substrates.
In order to test the reliability of the substrates before manufacturing and assembling expensive production versions, samples of the substrates called test coupons are manufactured and subjected to pre-qualification tests to discover faults in the production process and to project the reliability and life of the substrates. The most critical and expensive test is to put the test coupons under bias, moisture, and high-temperature conditions, which is referred to as a Bias/Humidity/Temperature (BHT) test, including some highly accelerated versions known as (HAST).
The test coupons typically have all of the critical dimensions of the production substrate, but are simplified. They do not typically contain all of the vulnerable test structures on one coupon. They are not strategically placed on a palate to capture faults that are heterogeneously distributed on a palate.
Although substrate manufacturers have used test coupons for some time, the use of traditional test coupons has disadvantages. Substrates are manufactured on a large palate with usually 40-50 substrates per palate, similar to chips on a wafer. One disadvantage is that problems that may arise during manufacturing of the substrates may not have a homogeneous fault distribution. For example, a manufacturing process may cause isolated faults on the left side of a palate, but the problem may not be detected if only one coupon on the right side of the palate is made. This reflects a typical manufacturing fault distribution issue.
Another disadvantage is that the Bias/Humidity/Temperature test requires special boards and sockets on which to connect the test coupons and to place in a test chamber. Typically forty-four test coupons are required to perform a qualification test. Each type of test coupon, however, requires a different type of connection, and each test coupon must be hand soldered to the sockets. Due to the number of test coupons needed to obtain a statistically valid evaluation and the number of connections per coupon, hand soldering increases the time and expense the testing.
Accordingly, what is needed is an improved method for performing pre-qualification test on flip-chip organic substrates.
The present invention provides a universal test coupon for performing pre-qualification test on a substrate. The test coupon includes at least two substrate test structures, and an edge connector for providing external electrical connections. Traces patterned on the test coupon connect the test structures with the edge connector, such that a test apparatus maybe coupled to the edge connector for testing the test coupon without the need to manually solder connections to the test coupon.
According to the system and method disclosed herein, the universal test coupon more accurately represents the distribution of quality of the fabrication process due to the multiple test structures incorporated into the test coupon. In addition, the incorporation of an edge card connector on the test coupon eliminates the need to hand solder the test coupon for pre-qualification testing. The universal test coupon may also be used to perform the actual qualification of certain process changes in substrate construction and to monitor production lot quality and reliability.